The present invention relates to a drive train for a motor vehicle, having a drive unit which comprises a prime mover, a multi-step transmission which comprises a transmission input and a first sub-transmission as well as a second sub-transmission, and having a power-splitting device which distributes the driving power between a first and a second drive shaft of a driven axle.
A drive train of this kind is generally known in the form of a so-called du-al-clutch transmission, for example. In this kind of drive train the prime mover is connected to the multi-step transmission via a dual-clutch arrangement, as is disclosed in document DE 103 05 639 A1, for example. An output of the multi-step transmission is connected to a power-splitting device in the form of a mechanical differential.
In this kind of drive train the transmission input is formed by two shafts concentric to one another, which are connected to the respective sub-transmissions. The mechanical differential does not allow any torque vectoring, in other words a differing distribution of torques to the driven wheels on the driven axle.
An idea of this kind is disclosed in the document DE 39 00 638 C2. In this case, an output from a multi-step transmission is connected to a mechanical differential and also to the drive shafts via transmission ratios and friction clutches that can be independently activated for the two drive shafts. By activating one of the friction clutches while cornering, the outside wheel may be driven at a higher speed, in order to achieve the torque vectoring effect.
In addition, a drive train is disclosed in document DE 10 2004 046 008 A1, in which a power-splitting device of a driven axle comprises two friction clutches instead of a mechanical differential, said friction clutches being activatable independently of one another. With a drive train of this kind, the driven wheels of a driven axle may be exposed to different torques, in order to achieve torque vectoring. An increase in the speed of the outside wheel is only conceivable in the case of a four-wheel drive train, however, in which this kind of dual-clutch differential is configured as a hang-on clutch, which can be shifted via a higher ratio than the other driven axle in the power flow.
The aforementioned drive trains are particularly used in conjunction with prime movers in the form of internal combustion engines. In this case, it is known for traditional drive trains to be additionally equipped with one or a plurality of electric motors, in order to set up a hybrid drive train.
In addition, a drive train is disclosed in document DE 199 17 724 A1, which is designed to be driven solely by an electric motor. The drive train comprises a multi-step transmission with two ratios, wherein the ratios are formed by wheel sets. The loose wheels of these wheel sets can be connected via friction clutches in the power flow, so that gear changes can be performed under load without any loss of tractive force. The output of the multi-step transmission is directly connected to a mechanical differential, which traditionally distributes the driving power between the two drive shafts.